1. Technical Field
The present invention relates to piezoelectric acoustic transducers, and relates more particularly to a piezoelectric acoustic transducer that achieves both compactness and increase in bass reproduction ability.
2. Description of the Related Art
A conventional piezoelectric acoustic transducer (also called as a “piezoelectric speaker”) reproduces sound, using: bending deformation of a diaphragm taking advantage of an inverse piezoelectric effect, and a resonance unique to each diaphragm. This has a problem of inferior bass reproduction ability compared to an electrodynamic speaker including a diaphragm having an equivalent area. A means to solve this problem is a piezoelectric speaker including a damper and an edge between a frame and a diaphragm (See, for example, Japanese Unexamined Patent Application Publication No. 2001-160999).
FIG. 28 is an external view of a piezoelectric speaker described in JP 2001-160999. The piezoelectric speaker 10 includes: an outer frame 21, an inner frame 22, a piezoelectric element 30, diaphragms 41, 42, 43, and 44, dampers 51, 52, 53, 54, 55, 56, 57, and 58, and edges 61, 62, 63, and 64. In the piezoelectric speaker 10, when applying an AC (alternating-current) signal in a direction perpendicular to a main surface of the piezoelectric element 30, the piezoelectric element 30 expands or contracts, in the direction of the main surface due to an inverse piezoelectric effect, thus causing bending deformation in the diaphragms 41, 42, 43, and 44. As a result, the piezoelectric speaker 10 generates a sound wave in a direction perpendicular to the main surface of the piezoelectric element 30.
The piezoelectric speaker 10 configured as above includes dampers 51 to 58 and edges 61 and 64, which allows reducing stiffness of a suspension system. Accordingly, the configuration allows reducing the minimum resonance frequency, and thus allows lowering a bass reproduction limit compared to a conventional piezoelectric speaker.